Sanders has been closing in on Clinton this past month in the Iowa and Hew Hampshire polls, and what looked like a long-shot candidacy at the outset now has the potential to capture the first two states. The Iowa caucus is nearing on Feb. 1, and the New Hampshire primary being held Feb. 9.

“[This week] he had better numbers against any of the Republicans than she did. He is more electable in a general election according to what people think now,” Mitchell said.

In response to Mitchell, Vilsack, who endorsed Clinton last year, insinuates Sanders’ lead in the polls is a result from the lack of negative Sander’s ads.

Sanders, who claims to have never run a negative ad, took down a digital ad from his website this past December, saying the ad fell in a “grey area.” The advertisement portrayed Hillary Clinton as a candidate who is backed by big banks and “other big money interests,” a criticism that has been widely used against Clinton.

“There has not been a negative ad directed at Bernie Sanders yet,” Vilsack said. “I guarantee you there will be plenty of negative advertising that will redefine Bernie Sanders.”

During the interview, Vilsack showed continued support for the Democratic nominee, saying “Hillary Clinton has withstood pressure over the course of her incredible career.”